The present invention relates generally to a blade for a gas turbine engine and, more particularly, to an apparatus and method of retaining such gas turbine engine blade in a predetermined position and orientation so that machining operations may be performed thereon in a consistent manner.
Manufacturing methods for gas turbine engine blades, and particularly the dovetails thereof, have typically been designed for batch production. While this approach has been thought to increase production, complex and expensive equipment is oftentimes required to accomplish the method. The grinding of finished dovetail shapes for airfoil blades is also an iterative and highly labor intensive process. If the desired dimensional results are not achieved for a particular test or tryout blade from a batch, the whole batch of such blades is scrapped and a new iteration cycle commences. This obviously can lead to a high level of manufacturing losses and overall process inefficiency.
Accordingly, a single piece flow concept has emerged as a simpler and more efficient approach to machining finished dovetail shapes for gas turbine engine blades. This approach has the added benefit of eliminating the low melt alloy matrix material utilized for encapsulating the airfoil shape while the blades are ground, which are known to contain environmentally unfriendly substances. In order to take advantage of the single piece flow concept, however, a device for retaining a gas turbine engine blade in a desirable position and orientation for the dovetail grinding operation to be accomplished is required. Such device should be configured so as to permit easy access to the root portion of the blade while holding the blade in a consistent manner which does not deform the airfoil portion. Further, orientation of the blade within the device must be highly accurate for a given class or size of blades.
Various types of retention devices and orientation systems for a gas turbine engine blade are known in the art, as seen by U.S. Pat. Nos. 6,017,263, 6,068,541, 6,139,412 and 6,287,182 to Dwyer. As seen therein, however, certain manufacturing operations must be performed on the gas turbine engine blades themselves so as to provide locating notches and guides. This serves to complicate the initial aspect of the process, as well as creates the need for additional finishing steps after the dovetail is formed. It will also be appreciated that access to the root portion of the blade is not without obstructions since clamping of the blade occurs at such location.
Another fixture for holding gas turbine engine blades is disclosed in U.S. Pat. Nos. 4,638,602 and 4,829,720 to Cavalieri. While access to the root portion of the blade is improved in such fixtures, the manner in which the blade is clamped in position (i.e., via a longitudinal pin which abuts against the datum point of the blade) can potentially cause deformation of the airfoil portion. This stems from a lack of mating to a substantial portion of the pressure and suction surfaces of the airfoil portion. Further, the limited point of clamping contact with the blade may create inconsistent positioning between blades held in such device.
While the aforementioned devices and methods of retaining a gas turbine engine blade are useful for their particular purpose, it would be desirable for an apparatus and method of retaining gas turbine engine blades to be developed which consistently positions a given size of blades in a predetermined orientation, provides easy access for machining operations, and enables easy insertion and removal of a blade therefrom. It would also be desirable for such retention device to be simple, inexpensive, reduce associated tooling costs, and allow use of smaller and less expensive machines.